Tunning pore filling of anodic alumina templates by accurate control of the bottom barrier layer thickness

Abstract

The role of the alumina barrier layer thickness (δ(b)) on the growth of Ni nanowires (NWs) in porous anodic alumina (PAA) has been revealed. By varying the final anodization voltage to form dendrites at the bottom of the nanoporous structure, we are able to optimize δ(b) (in the 2-16 nm range), allowing us to obtain a Ni pore filling percentage (f(p)) of almost 100% for δ(b) = 10 nm. However, deviations from this optimal δ(b)-value led to a strong decrease of f(p). Moreover, an increase of the electrodeposition efficiency (EE) and NW homogeneity was also verified for δ(b) up to 10 nm. Such increase in nominal δ(b) leads to a consistent growth rate in all pores and consequently a complete and uniform nanopore filling. On the other hand, the decrease in electrodeposition efficiency visible for δ(b) > 10 nm is related with hydrogen evolution and dielectric breakdown of the insulator layer due to the required high deposition voltages. Non-uniform NW growth is then visible, with the consequent decrease in f(p). The control of the pore filling and length homogeneity of the fabricated 1D metallic nanostructures, combined with the ability to adjust the pore dimensions of PAA, can bring novel approaches for the fabrication of nano-objects and thus exciting new applications.

Magnetic interactions and reversal mechanisms in Co nanowire and nanotube arrays

“…The milling process was carried out using an ion beam sputter deposition system by Commonwealth Scientific Corporation. 21 The angular dependent magnetic hysteresis loops and FORC measurements were performed in a vibrating sample magnetometer (VSM; LOT-Oriel EV7) at room temperature. For all the magnetic measurements, the samples were saturated under a maximum applied magnetic field of 15 kOe.…”

“…[19][20][21] For the fabrication of large arrays of metallic NWs and NTs, potentiostatic electrodeposition in NpATs has proved to be a low cost and high yield technique. 22 Varying the deposition conditions (time, applied potential and electrolyte temperature, pH, and concentration), we can also tune the crystallographic structure and metal alloy composition, changing the respective physical response.…”

Ultra-long Fe nanowires by pulsed electrodeposition with full filling of alumina templates

“…To our knowledge, only low thickness (few micrometers) templates have been used to fabricate Fe NWs and with filling fractions far from 100%. In this work we focus on the electrodeposition of Fe NWs inside alumina templates synthesized with oxalic acid (standard conditions [10]). …”

“…Recent results demonstrated [8,10,[21][22][23] that pulsed electrodeposition (PED), is an excellent alternative to the two previous methods. In PED, the reduction of the PAA barrier layer is not performed by chemical etching, which isotropically attacks the alumina, hence reducing the wall and barrier layer thickness alike, usually leading to low PAA homogeneity.…”

“…A different approach relies on the linear dependence between the anodization voltage and pore diameter, inter pore distance and δb [20,[23][24][25] , respectively, for the used pH, temperature and electrolyte) [26]. This method allows reducing the barrier layer thickness without changing the diameter of the main pore [8,10]. Using a non-steady-state anodization we were able to accurately tune δb by controlling the final anodization voltage.…”